Nowadays navigation systems have become standard equipment for vehicles, for example, automobiles. Usually such systems receive GPS (Global Positioning System)—satellite radio signals. These radio signals are received by a GPS antenna of the vehicle and are provided to a navigation computer in the vehicle. This computer processes the received data and furthermore data obtained by motion sensors, as wheel sensors and gyroscopes, and thus, determines the present position of the vehicle.
Known navigation systems typically use electronic maps to represent cartographic features, as streets, buildings and rivers, and make use of a medium such as a compact disk or a digital video disc to store the data that relates to the cartographic features. After map matching the present position of the user is indicated in the digital map. By acoustic and/or visualized information the user is guided to the predetermined destination.
Some navigation systems are able to display detailed digital maps and/or three-dimensional detailed views indicating routes to predetermined destinations, the types of manoeuvres to be taken at various locations as Junctions as well as different kinds of points of interest (POI) as, for example, gas stations, hotels or restaurants and also landmarks.
In order to provide the navigation functions navigation systems make use of one or more detailed databases that may comprise bitmap images for lanes, sign post information, landmarks etc. and data which, e.g., represent physical features of a geographic region and points of interest.
In principle, a route from a starting point to a destination point can be calculated by an in-vehicle navigation system or externally by some computing center that has more computational power, always updated databases and real-time information, for example, traffic information. If a route for route guidance is calculated at the computing center it has to be encoded and transmitted to the in-vehicle navigation system where it is to be decoded for the actual route guidance, for example, route display. Encoding and decoding are necessary since each execution environment (the in-vehicle navigation system and the computing center) has its own navigation database and will be able to calculate and present routes only that have references to their own navigation database. Moreover, different data formats may be employed in different execution environments. Thus, any communication between the different execution environments has to be based on encoding and decoding of data.
During encoding the calculated route is converted from a database-dependent description to a database-independent description and during decoding the route is converted from a database-independent description to a database-dependent description.
In the art, the processes of encoding and decoding are rather time-consuming, for example, due to expansive attributes of route data needed for the encoding/decoding and detailed road network descriptions included in the navigation databases used for the route finding process. In particular, in the case of long-distance routes the decoding of received encoded routes result in a high computational load on in-vehicle navigation systems and large time delays between a request for route guidance and the presentation of an externally calculated route.
It is therefore a problem underlying the present invention to provide route guidance and, in particular, encoding and decoding of routes, that is less time consuming as in the art but allows for a reliable communication of route data from one execution environment to another.